On May 29, 1983, the well-known Thai entomologist, Bro. Amnuay Pinratana (Bangkok), informed us of his current work on a checklist of the Odonata of Thailand. In support of this valuable project we have prepared (June 27, 1983) a list of species examined cytologically during our two brief visits to that country, in early April and late May, 1979, and which includes a few cytologically highly interesting species. As often before, the specimens were kindly checked by Dr M.A. LIEFT1NCK (Rhenen, The Netherlands), who informed us (December 21) 1980) that the material includes a number of probably undescribed taxa. Circumstances beyond our control prevent us for the time being to work out this material in detail. For the sake of record, therefore, we now present a preliminary list of male haploid chromosome numbers only. A full account will appear elsewhere at a later dale. The 13 asterisked (♦) species are new to cytology. The locality data are as follows: (I) Pha-lad, Chiang Mai: a cascading stream, alt. 420 m approx., April 4-5; — (2) Huey-Kaew, Chiang Mai: a waterfall, alt. 320 m approx.. April 4-6; — (3) Phai-Hin stream, Chiang Mai. alt. 320 m approx., April 4; — (4) near the west bridge of Huey-Kaew arboretum: running and stagnant water, April 4-6; — (5) Chulalongkorn University Campus, Bangkok: park ponds, May 11, 25; — (6) large pond near the Erawan Hotel, Bangkok, April 2.